UI tests for accessing contents via the SharedArrayBuffer

[jtpio]

As a follow-up to #87, we should check if it's possible to test accessing the contents with the new approach via the SharedArrayBuffer.

Maybe by using an addition server via the Playwright webServer config section, with a server that enables the COOP / COEP headers:

xeus/ui-tests/playwright.config.js

Lines 15 to 22 in 22278fc

	webServer: [
	{
	command: 'yarn start',
	port: 8000,
	timeout: 120 * 1000,
	reuseExistingServer: true
	}
	]